US10004472B2ActiveUtilityA1
Pet detector timing calibration
Est. expiryOct 27, 2034(~8.3 yrs left)· nominal 20-yr term from priority
A61B 6/4266A61B 6/583A61B 6/585G01T 1/2985A61B 6/037
47
PatentIndex Score
0
Cited by
9
References
16
Claims
Abstract
A diagnostic imaging system includes a plurality of radiation detectors ( 20 ) configured to detect radiation events emanating from an imaging region. The system includes a calibration phantom ( 14 ) configured to be disposed in the imaging region spanning substantially an entire field of view and to generate radiation event pairs that define lines-of-response, wherein the calibration phantom is thin such that each LOR intersects the calibration phantom along its length, the thickness of the phantom being smaller than the length of the LORs. A calibration processor ( 24 ) receives input of the radiation detectors and calculates an incidence angle independent crystal delay T i for each detector. The calibration processor ( 24 ) constructs a first look-up table for the timing correction of each LOR and a second look-up table for the angle depth of interaction correction for each crystal by combining T i and η i .
Claims
exact text as granted — not AI-modifiedThe invention claimed is:
1. A diagnostic imaging system, comprising:
a plurality of radiation detectors configured to detect radiation events emanating from an imaging region;
a calibration phantom configured to be disposed in the imaging region spanning substantially a length and width of a field of view and to generate radiation event pairs that define lines-of-response, wherein the calibration phantom includes a sheet source such that each LOR intersects the calibration phantom; and
a calibration processor configured to receive input from the radiation detectors and calculate an incidence angle dependent crystal delay τ i , for each detector.
2. The system according to claim 1 , wherein the calibration phantom is configured to be disposed in the imaging region at offset orientations during calibration.
3. The system according to claim 1 , wherein the calibration processor is configured to determine the orientation and location of the calibration phantom in the field of view and at least one intersection of the phantom and each LOR.
4. The system according to claim 3 , wherein the calibration processor is further configured to calculate the difference between an actual detection time and an expected detection time.
5. The system according to claim 4 , wherein the calibration processor further configured to iteratively calculate a crystal delay using
τ
i
(
n
+
1
)
=
(
1
-
α
)
τ
i
(
n
)
+
α
∑
j
n
ij
(
E
ij
-
M
ij
_
+
τ
j
(
n
)
)
∑
j
n
ij
,
wherein i and j are crystal indices, α is a dumping factor, E is the expected time difference, M is the mean measured time difference, n is the number of events.
6. The system according to claim 4 , wherein the calibration processor is further configured to substitute E with E′ into the iterative calculation, such that E′ ij =(E ij −η i (ϕ ij )+η j (ϕ ji )) wherein ϕ ij is the gamma incidence angle to crystal i and η i is the incidence angle dependent timing adjustment for crystal i.
7. The system according to claim 1 , wherein the calibration processor is further configured to construct a first look-up table for the timing correction of each LOR and a second look-up table for the angle depth of interaction correction for each crystal by combining τ i and η i .
8. A method for calibrating a diagnostic imaging system, comprising:
disposing a calibration phantom in an imaging region spanning substantially an entire field of view and to generate radiation event pairs that define lines-of-response (LOR), wherein the calibration phantom spans a length and width of a field of view such that each LOR intersects the calibration phantom;
detecting a plurality of radiation events emanating from the imaging region;
receiving input of the radiation detectors;
determining a location of the phantom along each LOR; and
calculating an incidence angle independent crystal delay τ i , based on the received input.
9. The method according to claim 8 , comprising:
acquiring a first list mode acquisition wherein the calibration phantom is sized and oriented to maximize the number of LORs going through it during the first list mode acquisition.
10. The method according to claim 8 , comprising:
disposing the calibration phantom in the imaging region at substantially 90 degrees offset orientations during calibration, wherein the phantom is planar.
11. The method according to claim 8 , comprising:
determining the orientation and location of the calibration phantom in the field of view and at least one intersection of the phantom and each LOR.
12. The method according to claim 8 , comprising:
calculating the difference between an actual detection time and an expected detection time.
13. The method according to claim 8 , comprising:
iteratively calculating a crystal delay using
τ
i
(
n
+
1
)
=
(
1
-
α
)
τ
i
(
n
)
+
α
∑
j
n
ij
(
E
ij
-
M
ij
_
+
τ
j
(
n
)
)
∑
j
n
ij
,
wherein i and j are crystal indices, a is a dumping factor, E is the expected time difference, M is the mean measured time difference, n is the number of events.
14. The method according to 13 , comprising:
substituting E with E′ into the iterative calculation, such that E′ ij =(E ij −η i (ϕ ij )+η j (ϕ ji )) wherein ϕ ij is the gamma incidence angle to crystal i and η i is the incidence angle dependent timing adjustment for crystal i.
15. The method according to claim 8 , comprising:
constructing a first look-up table for the timing correction of each LOR by combining τ i and η i ; and
constructing a second look-up table for the angle depth of interaction correction for each crystal.
16. A diagnostic imaging system comprising:
a plurality of radiation detectors disposed around an imaging region configured to detect radiation events emanating from the imaging region, the detectors having differing timing delays;
a calibration phantom configured to be disposed in the imaging region the phantom including radiation sources which emit pairs of oppositely traveling radiation events which interact with the radiation detectors and define an LOR, the phantom being at a known location along each LOR; and
one or more processors configured to:
receive outputs from the detectors and, from the known location and a relative time of the detector outputs to determine temporal correction factors for the detectors which correct for the differing timing delays among the detectors,
construct a first look-up table for the temporal correction factors of each LOR and a second look-up table for the angle of incidence dependent depth of interaction correction for each crystal using an iterative calculation of an incidence angle independent crystal delay τ i , and
reconstruct images from the LORs with localization along each LOR based on the relative time of the detector output using the look-up tables to correct the relative times of the detector outputs.Cited by (0)
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